Aircraft air-conditioning systems having compressors operated with ambient air are known in different embodiments. An aircraft air-conditioning system is known from WO 2005/030583 A1 which has three heat exchangers which are located in a ram air duct and can be connected to achieve different cooling capacities and thus different cooling of the compressed air in different manners.
An aircraft air-conditioning system is known from DE 102 34 968 A1 in which a pre-cooled bleed air flow is combined with a compressed and pre-cooled ambient air flow to form a mixed air flow which is then supplied to suitable means for the dehumidification of this mixed air flow. The means for the dehumidification of the mixed air flow consist of a combined evaporator/condenser unit through which the two airflows mixed at the mixing point are guided while increasing the size of the droplets contained therein. A further aircraft air-conditioning system is known from DE 103 50 541 A1 which is operated without bleed air and whose compressors are charged with ram air or ambient air and are driven by means of motors.
There is a problem with compressors charged with ambient air in that the ambient conditions, in particular the pressure of the compressor inlet air, vary considerably in dependence on the flight altitude. A large demanded operation range results from this which cannot be covered completely in an efficient manner by one compressor.
It is therefore the object of the present disclosure to further develop a method of operating an aircraft air-conditioning system such that the pressurization, temperature control and fresh air supply of an aircraft cabin are ensured in an efficient manner independently of the flight altitude.
This object is solved by a method of operating an aircraft system, with only a first compressed air source in communication with the aircraft cabin in a first operating mode and for both the first compressed air source and a second compressed air source in communication with the aircraft cabin in a second operating mode. The selection of the operating mode depends at least on the pressure of the ambient air such that the first operating mode is set at a high pressure of the ambient air and the second operating mode is set at a pressure of the ambient air lower in comparison. The method in accordance with the present disclosure thus works in two, or more than two, operating modes which can depend on the flight altitude and thus on the pressure of the ambient air.
In the first operating mode, the air supply is effected only with the named first compressor which can, for example, be a single-stage or also a multistage compressor. This compressor guarantees the demands on pressurization, temperature control and fresh air supply in ground operation.
In a second operating mode, that is at lower ambient pressures such as occur in flight, the demanded fresh air mass flow is made available by at least two sources. These are the named first compressor, which is charged with ambient air and is driven by means of a motor and/or of a turbine, and a further compressed air source. Provision is preferably made for the two mass flows of the compressed air sources to be mixed and thus to be supplied to the further treatment, that is cooling and dehumidification, for example, before the mixed air flow conditioned in this way is supplied to the aircraft cabin.
It is preferred for the air to be subjected to cooling prior to the entry into the aircraft cabin, with the cooling taking place by at least one ram air heat exchanger located in a ram air duct of the aircraft and/or by at least one turbine. In the first operating mode, the cooling preferably takes place both by the at least one ram air heat exchanger and by means of one or more expansion turbines integrated in the cooling process, with them preferably being coupled on a shaft to the first compressor and to the motor. One or more turbines can thus be located on the shaft with the compressor. The cooling is preferably realized by means of only one machine which is integrated in the cooling process in this way and which can have one or more turbines.
The arrangement of a plurality of expansion stages, i.e. turbines, with the compressor on one shaft has the advantage that, for example, one of the turbines can be utilized for the cooling and another turbine can be utilized for another purpose, for example for the energy recovery by the expansion of cabin air. The case is likewise naturally possible that all the turbines of an air-cycle-machine (ACM), which is an arrangement of several components located on the same shaft, are used for cooling purposes. The utilization of the individual expansion stages for different purposes can depend, for example, on certain parameters and must therefore not be identical under all conditions.
In the second operating mode, provision is preferably made for the outlet air of the first compressed air source and at least some of the outlet air of the second compressed air source to be mixed and for the mixed air flow to be subjected to cooling. The cooling can be realized as in the first operating mode by at least one ram air heat exchanger and by means of at least one expansion turbine integrated in the cooling process.
The mixing point of both flows can for example be formed by a chamber, e.g. by a chamber for the conversion of ozone or hydrocarbons.
Provision is made in a further aspect of the present disclosure for the outlet air of the first and/or second compressors or of the second compressed air source to be supplied to a jet pump at least in part. This jet pump can be arranged, for example, in the ram air duct of the aircraft and can serve the cooling of a ram air heat exchanger and/or the cooling of the motors driving the compressors.
The second compressed air source can be formed by one or more motorized single-stage or multistage second compressors charged with ambient air, ram air and/or precompressed air. It is likewise possible for the second compressed air source to be formed by engine bleed air.
The present disclosure is not restricted to a first and a second compressed air source. Any desired number of further compressed air sources can rather be connected in.
In a preferred aspect of the present disclosure, the first compressed air source and the at least one further compressed air source are connected in parallel. The compressed air sources can thus, for example, be compressors connected in parallel and charged with ambient air.
The present disclosure does not only have the advantage of efficient operation of an aircraft system in particular for the purpose of fresh air supply, air conditioning and pressurization of an aircraft cabin. A further substantial advantage may result from the redundancy based on the at least two compressed air sources per system. If, for example, the motor of one of the compressors is defective, a sufficient supply of the aircraft cabin is nevertheless provided by the other compressed air source both in ground operation and in flight operation. Redundancy also results in the case of two aircraft systems or of two aircraft air-conditioning systems which communicate with one another between themselves by means of a line (cross bleed ducting), as will be explained in more detail below.
The above recitations with respect to the first and second or further operating modes apply to the normal case. In the effect of a defect, such as on the failure of the first compressor, other connections can be made which differ from this. If, for example, the first compressor fails, provision can be made for the supply of the aircraft cabin to be carried out by means of the second compressed air source, even if the first operating mode would actually have to be selected at the prevailing ambient conditions.
In a further aspect of the present disclosure, provision is made for a water extraction circuit to be provided downstream of the compressed air sources and upstream of the cabin as well as for a turbine to be provided downstream of the water extraction circuit and for a third operating mode to be provided in which both the first and the second compressed air sources are in communication with the aircraft cabin and in which the compressed air is guided around the water extraction circuit and the turbine in a partial or complete bypass. The provision of fresh air first takes place in this mode as in the first or second operating modes. However, due to the ambient conditions at a high flight altitude, the water extraction circuit and the turbine stage can be bypassed at least partially by opening a bypass valve. Cooling now takes place in this case substantially via the ram air heat exchanger or exchangers.
Provision is made in a further aspect of the present disclosure for the air to be subjected to cooling prior to entry into the aircraft cabin, with the cooling taking place by at least one ram air heat exchanger located in a ram air duct of the aircraft and by one or more expansion turbines which are charged completely or partially and which are seated with the first compressor on a shaft. Provision is preferably made for the cooling to be realized in addition to the ram air heat exchanger or exchangers by means of only one ACM which is integrated in the cooling air process and which can in turn have one or more turbines. This turbine or these turbines is/are preferably coupled to the compressor and the motor on a shaft.
Since the second or the further compressed air sources are preferably only switched in from a certain altitude in flight in accordance with the present disclosure, they can be used at least partially for the demand of the cooling air for the ram air heat exchangers on the ground, that is in the first operating mode.
It is possible in this process for the compressor extracted air to be supplied via regulation valves or check valves partially or exclusively to a jet pump integrated in the fan chamber of the ram air duct. This jet pump ensures the cooling air flow via the ram air heat exchangers. The jet pump can be made with sound-absorbing measures such as a specific shape of the flow cross-section and/or specific sound-absorbing layers. It is generally also possible to connect the second compressed air source to a jet pump in a different operating mode to the first operating mode. Generally, the first compressor can also be in communication with a jet pump irrespective of the operating mode.
It is likewise possible for an impeller, which is integrated in the ram air duct or the fan chamber (plenum), to be utilized for the suction of ambient air via the ram air heat exchanger or exchangers. The impeller is coupled with the motor compressor on a shaft. The air transported by the compressor which is also running in this solution can either be blown out to ambient or be utilized in the ram air duct for the support of the fan via a jet pump or be supplied to further consumers.
It is further possible to arrange one or more fans independently of the compressor or compressors. One or more fans can thus be provided which are used for the cooling of the compressor motor or motors and/or of the ram air heat exchanger or exchangers and which are not coupled to the compressors or are not seated with them on a shaft.
The fan chamber can have branches in the flow guidance. Provision can be made in this process for the ram air duct to have one or more partition walls extending in the flow direction at least sectionally which divide the ram air duct into at least two sections, with a jet pump communicating with the second compressed air source or an impeller coupled to the second compressor being arranged in the first section and with the second section representing a bypass of the first section for the air flowing through the ram air duct. The cooling air of the ram air heat exchangers is preferably transported under ground conditions in the first section. The jet pump and the impeller are arranged in this section, with them being able to be arranged jointly in one branch or separately in adjacent branches. The cooling air of the ram air heat exchangers is preferably transported under flight conditions in the second section. A bypass of the jet pump or of the impeller thus results whereby the transmission is increased. This bypass—or another branch—supports the secure ventilator operation in which a recirculation flow is enabled, provided the fan is coupled to a compressor.
A further section can be provided in the ram air duct in which a jet pump and/or a fan is/are arranged for the purpose of cooling the motors driving the compressors.
Provision is thus made in a further aspect of the present disclosure for a jet pump or a fan to be provided for the purpose of cooling one or more motors driving the compressor or compressors.
The time of the switching in of the parallel compressors or compressed air sources can depend on different criteria.
It is possible to switch over from the first to the second operating mode when the packing limit of the first compressor is reached or when the maximum motor power of the first compressor is reached. Providing the same motor size with all compressors is possible, which requires an earlier switching in of the additional compressors.
When the second compressor or the second or a further compressed air source per pack is switched in, a halving/reduction of the mass flow for the first compressor takes place since the second compressor or the further compressed air source now transports the mass flow now lacking to cover the required fresh air amount. This can have the result that the new operating point can lie in the instable range to the left of the pump limit (surge line) at least for the first compressor. Different measures can be taken to enable a secure, that is stable, operation.
It is possible to increase the fresh air amount for the cabin in the second operating mode and also in the third operating mode. An increase in the fresh air amount is generally also possible in other operating modes, e.g. in the first operating mode.
It is likewise possible to increase the mass flow via the compressor stages through recirculation, with a valve (anti-surge valve (ASV)) being able to be arranged in the recirculation line. This increase in throughflow does not serve the increase in the fresh air amount, but only the component security. Such a recirculation is possible irrespective of the operating mode, i.e. it can be selected in the first, second, third operating modes, etc.
It is furthermore possible that, in the first or second operating mode, the outlet air of the first compressor and/or of the compressors is supplied to the second compressed air source and/or to a further compressed air source via a jet pump via the ram air duct of the aircraft or to further consumers of the aircraft. This method of operation is possible in the first or second operating modes, but also in other operating modes.
This also results in operation of the compressors in the stable range for any desired mode.
These further consumers can, for example be the systems OBOGS, OBIGGS, WAI (wing anti-ice) or a further heating/cooling. It is furthermore possible to utilize the outlet air for the engine start or for the start of an auxiliary engine (APU).
To limit the required motor power, the transmission of the pack can be increased in dependence on the demanded cooling capacity and on the air dehumidification via the water extraction circuit. Different possibilities are available for this purpose:
It is possible to adapt the required motor power ideally via a variable turbine guidance apparatus via an adaptation of the cross-sectional area. The important design point for the turbine nozzle is the ground case with maximum cooling capacity and high air humidity. As the flight altitude increases, an increase in the size of the nozzle area is necessary. The control of this turbine guide apparatus can take place, for example, electrically, electropneumatically or also purely pneumatically.
The transmission can furthermore be increased in that a bypass line is opened at a large flight altitude at low ambient humidity which bypasses the water extraction circuit and the turbine. This is possible because additional dehumidification is not necessary at high flight altitudes. The valve BPV is arranged in this bypass line. With a fully open BPV, the required cooling capacity must be achieved by the ram air heat exchanger since the turbine stage is almost completely bypassed due to the higher transmission of the bypass line. If a higher cooling capacity is necessary, the BPV may only move into regulation to achieve additional turbine cooling capacity or other cooling capacity, whereby a higher pressure ratio of the compressors and thus more motor power is required.
Provision can further be made for a common control unit to be provided for the valve TCV, which is disposed in a line which connects the outlet of the compressed air source or the mixed air line to the outlet of the turbine, and for this guide apparatus, whereby only one single actuator is required for this control.
On the ground and at a low flight altitude, it can be necessary to take suitable measures to increase the heating capacity of the air-conditioning system. Different possibilities are likewise available for this purpose.
It is possible to allow some of the compressed air to recirculate via the compressors for the purpose of increasing temperature, whereby the temperature of the process air is increased and thus the heating capability of the air-conditioning system is also increased.
It is likewise possible to increase the outlet temperature by a valve for the throttling of the compressors and, on the other hand, to enable a bypass of the turbine stage.
It is furthermore possible to design the guide apparatus of the turbine via variable changes in the cross-sectional surface such that the heating capability of the air-conditioning system is also thereby ensured under ground conditions.
It is furthermore possible to influence the heating capacity in that the ram air amount is reduced. This can take place in that the ram air duct is closed partially or fully by means of a flap or valve controlled via an actuator. It is likewise possible to reduce or cut off the compressed air supplying the jet pump located in the ram air duct or to change the pressure level and the throughput.
A further possibility consists of adapting the power of the impeller located in the ram air duct.
The motor cooling can be realized by the use of ambient air or ram air or by means of a liquid coolant circuit or two-phase coolant circuit. A separate jet pump must optionally be provided for the motor cooling duct. The cooling can take place by means of ambient air or ram air.
The water extraction circuit of the air-conditioning system may include a reheater, a condenser downstream of it on the compressed air side and a water extractor downstream of it. This water extraction circuit can generally also be designed without a reheater.
Provision is made in a further aspect of the present disclosure for a first air-conditioning system and a second air-conditioning system to be arranged which are operated according to one or more of the above methods, with the second compressed air source being formed by two motorized compressors charged with ambient air, ram air or precompressed air or by two other compressed air sources such as engine bleed sources, with one of the second compressed air sources being switched in to both air-conditioning systems in the second operating mode and with the second compressed air sources being switched in to one each of the two air-conditioning systems in a further operating mode. Such a method has the advantage that the reduction in the mass flows for the first compressors of the air-conditioning system does not turn out to be so strong on the change from the first to the second operating mode since the mass flow of the switched in compressor or of the switched in compressed air source is first divided between both air-conditioning systems.
This effect can naturally also be realized in that the second compressed air source is only formed by a motorized compressor charged with ambient air, ram air or precompressed air or only by a bleed air source. This one second compressed air source can be switched in to both air-conditioning systems or both aircraft systems at reduced capacity in the second operating mode so that the reduction of the mass flow of the first compressor only turns out relatively low. In a further operating mode, the second compressed air source can be switched in to both air-conditioning systems with a mass flow higher in comparison.
The connection of second air-conditioning systems or aircraft systems by a connection line results in a likewise redundant design so that a fault case in one of the air-conditioning packs or systems can be compensated largely or completely.